Growing the perfect tomato is on the bucket list of many gardeners. For some, growing heirloom tomatoes takes that challenge up a notch. In 1946, the first hybrid tomato, 'Single Cross,' hit the market. At the time, the science of hybridizing was in its infancy, and the notion of improving traits such as yield and disease resistance were innovative and exciting. However, as more and more hybrids flooded garden center shelves, something happened: some tomatoes tasted bland, some had tough skins, and others were mealy or dry. The pendulum began to swing in the other direction, and today gardeners crave the tender, rich, juicy tomatoes their grandparents grew. These tomatoes are open-pollinated, meaning the seeds will produce plants identical to the parent plant, and have been around prior to 1960. These tomatoes thrived in the gardens of our ancestors without modern fertilizers or pesticides, and you can grow them too.

How to Grow Heirloom Tomato Plants

Heirloom tomato plants need a lot of nature's bounty to produce their yield. Don't skimp on light, water, or fertilizer if you want big beefsteaks to adorn your salads and sandwiches.

Light

When it comes to sunlight, heirloom tomatoes are one of the hungriest plants out there, along with plants like sunflowers or corn. These are plants that need full, direct sunlight all day long. Pay attention to any shadows cast by neighboring trees or buildings when you plan your tomato patch, and make sure your plants will get the benefit of a full day of unfiltered sun.

Soil

Healthy soil is a critical component of thriving heirloom tomato plants. Tomato plants will yield the greatest harvest in rich, loamy soil that allows roots to penetrate deeply. If your soil is heavy clay, use raised beds or container culture. Add compost, leaf mold, or manure up to 50% to blend with the native garden soil.

Water

Keeping your tomatoes well-watered is a must for heirloom tomatoes, especially once they set fruit. Watering deeply will encourage deep root systems. Assuming you did a good job preparing the soil, drainage should be excellent, so keep an eye on the moisture level and never let plants dry out. Allowing the soil to vacillate between moist and dry causes problems in fruit development, including cracking and blossom end rot. Use drip irrigation to further limit airborne diseases like blight.

Fertilizer

Heirloom tomatoes are heavy feeders, and need regular fertilizing to bloom and fruit. Organic or chemical balanced all-purpose fertilizer are both acceptable and a matter of personal preference.

Potting and Repotting

Use premium potting soil for potting tomatoes. Plants will need repotting frequently in warm weather, so check the drainage hole for roots to prevent plants from becoming root bound.

Propagating

Tomato cuttings root readily. As you prune away suckers, plant them in the soil or root them in water. They will form roots and begin to grow as separate plants within a week.

Varieties of Heirloom Tomatoes

There are hundreds of varieties of heirloom tomatoes, and the cultivar names are as colorful as the fruits themselves.

Brandywine is a gateway variety for many new to heirloom tomato gardening. The giant pinkish-red ruffled fruits, tender skin, and juicy complex flavor might remind you of a piece of Willy Wonka chewing gum: sweet, followed by tangy and spicy, followed by savory and umami flavors, all in one magnificent bite.

Black Krim tomatoes originated from Krim, Russia, and quickly gained a wide following with their sweet, robust flavor and handsome maroon fruits.

Aunt Ruby's German Green tomatoes stay green until harvest, which might fool hungry squirrels but not your tastebuds: these large beefsteak tomatoes are the perfect blend of sweet and tangy.

Brandywine Tomatoes.
Posinote/Getty Images

Black Krim Tomatoes.
Campbell Downie/Getty Images

Aunt Ruby's German Green Tomato.
cristina.sanvito/Flickr/CC BY 2.0

Toxicity of Heirloom Tomatoes

According to the ASPCA, tomato leaves are toxic to dogs, cats, and horses. Ingestion may cause severe gastrointestinal upset, weakness, or slow heart rate. Barring allergies, tomato fruits show no toxicity to any species.

Pruning

Pruning heirloom tomatoes can increase plant productivity in the garden. Remove suckers at the base of the plant to direct the plant's energy to producing fewer, but larger fruits. Heirloom tomatoes grow quite large and need staking for support. By reducing the number of fruiting branches down to four or five with pruning, your plants will be manageable and individual fruits will be larger than without pruning.

Harvesting

Heirloom tomatoes are ready to be picked just before their color peak. Leaving them on the vine too long encourages cracking. Tomatoes that stay green upon ripening can be a little tricky to judge; usually the color shifts from a flat mint green to a brighter chartreuse or streaky green. The fruits will also soften as they approach their peak.

Being Grown in Containers

Heirloom tomatoes growing in containers will need more frequent watering and fertilization than those growing in the ground. Use a large 24-inch pot for healthy root systems. Fertilize every two weeks with an all-purpose 10-10-10 fertilizer.

Growing From Seeds

Heirloom tomatoes are easy to grow from seed. Use moist, sterile potting mix, and press the seeds lightly into the soil. Germination takes place in about a week if temperatures are between 70 and 75 degrees F.

Heirloom Tomatoes vs. Hybrid Tomatoes

Heirloom tomatoes and hybrid tomatoes look the same and have the same growing requirements. However, you cannot save seeds from hybrids and expect them to grow true-to-type. Check your plant or seed packet labels if you wish to save seeds.